Monitoring of organ condition may be important after surgery such as organ transplantation and resection. Surgical complications, such as vascular complications, may disrupt adequate oxygen circulation to the tissue, which is critical to organ function and survival. Following liver surgery, for example, a physician may draw patient blood to determine the condition of the organ by measuring liver enzymes (such as transaminases) and clotting factors (such as prothrombin). Unfortunately, these blood tests reflect liver condition only at the time the blood sample is drawn, and changes in these laboratory values can often be detected only after significant organ damage has already occurred, permitting a limited opportunity for intervention by the physician to improve the condition of the organ or find a replacement organ in case of transplantation for the patient.
Other methodologies have been used to assess internal tissue conditions. For example, Doppler ultrasound techniques, angiography, implantable optical probes, and thermodilution catheters have been used to measure tissue oxygenation and/or perfusion. However, these techniques can be difficult to successfully apply to continuous monitoring of organ condition, and may provide only qualitative or indirect information regarding a condition, and/or may provide information about only a small segment of an organ.
Therefore, it is desirable to have a device and methods to aid physicians in predicting problems and complications associated with internal trauma or surgery. It is desirable to have a device which is positionable and removable with relatively minimal effort, minimally invasive and causes minimal discomfort for the patient, provides continuous current information about tissue or organ condition, provides direct information about tissue or organ condition, and/or provides feedback on the effects of interventions, such as medications or other procedures to improve tissue or organ. One convenient method for measuring the condition of internal tissues and organs is to embed optical reflectance sensors in a common surgical drain that is placed adjacent to the organ/tissue of interest during surgery.
Optical reflectance sensors involve the use of visible and/or near-infrared radiation to measure the absorbance of haemoglobin in a tissue bed to determine the oxygen saturation of hemoglobin. The optical absorption characteristics of the main oxygen carrier haemoglobin vary with its state of oxygenation. In general, an optical reflectance sensor illuminates the tissue with visible and/or near-infrared radiation and collects the reflected and/or backscattered light for spectral analysis to determine the state of tissue oxygenation. The oxygen saturation of hemoglobin can be estimated by measuring its optical absorption at predetermined wavelengths that allow the maximum distinction between oxyhemoglobin and deoxyhemoglobin. Certain reflectance sensors uses optical fibers to transmit the illumination light and collect the reflected light from the measurement location.
When such fiberoptic sensors are embedded in a surgical drain or in any other kind of probes to monitor adjacent tissues it may be required to adapt the tips or endings of such optical fibers to interrogate a tissue surface that is parallel to the axis of the optical fibers. This may be achieved by adjusting the tip of the optical fiber to allow the side-emission and/or side-collection of radiation to interrogate the adjacent tissues or organs. Micro mirrors and micro prisms may be fitted to the tip of the optical fibers to enable the side emission/collection of radiation to interrogate tissue, however, simpler and cheaper techniques are desired.